In a number of instances it is important to detect or determine what are the component materials of an article with a non-invasive, fast and accurate process.
For example, security focussed detection systems are important equipment in the transport and travel industries. Such detection equipment is employed to deter and detect smuggling and terrorist activities. In particular, aircraft passenger luggage (both carry-on and hold-shipped) and airfreight needs to be assessed quickly by such systems to maintain a high turnover of departures and arrivals of aircraft from an airport. Aircraft passengers in particular dislike having their air travel delayed by security procedures.
The most effective of these security measures is a physical search of cargo or the passengers themselves to detect the presence of contraband, weapons and explosives. However, such physical searches are slow and also an invasive process for passengers which are to be avoided if possible.
Scanning based equipment is used to a limited extent in the form of x-ray absorption systems to scan luggage and cargo. X-rays have a strong penetrating power which can be used to examine an entire piece of luggage quickly. However, such x-ray absorption based systems provide only limited information with respect to the composition of a target or, in particular, a piece of luggage under investigation. Such existing x-ray security scanners can provide general information in terms of the physical outline of an article present within a target which strongly absorbs x-rays. In particular, dual energy measurement scanning systems are known in such applications which can distinguish between received high energy and low energy x-rays. However these systems are limited in their ability to distinguish between different materials which compose a target. Such dual energy systems are in particular limited to assessing whether target material contains an inorganic, organic or metallic materials.
Such existing security scanners provide limited information as a consequence of their limited resolution of energy level. X-ray scanning systems are known for laboratory environments which can resolve a wide number and range of different energy levels for received x-rays. However, these types of laboratory equipment are comparatively expensive to purchase, require a high degree of maintenance and are also complicated to use. Such laboratory type equipment cannot readily be transplanted directly into environments where security based scanning equipment is required, and in particular cannot function in real time to provide results quickly. Generally the detector systems provided in such security x-ray scanners do not readily differentiate the energy levels of received x-rays, but simply indicate the amount of x-ray flux received which has been transmitted through a target at either a high or low energy level.
This characteristic of such dual energy x-ray absorption based detection systems explains why this technology is mostly used only to detect the presence of materials with inorganic compositions. In the case of explosives the compounds in question generally fall within the realms of organic chemistry, where the x-ray absorption characteristics of explosive materials can be very similar to those of other innocuous organic materials. Due to the limited ability of dual energy x-ray absorption systems to distinguish or resolve the energy level of received x-rays transmitted through such target, distinctions cannot easily be made with respect to any particular composition of a target.
This limitation of dual energy x-ray absorption technology also explains why it is not used in other composition determination applications. On-line or real time composition determination has many and varied uses outside of security applications such as, for example, in quality assurance for industrial processes, diagnosis scanning for veterinarian or medical procedures, or any other suitable application where the exact composition of the materials making up a target is not known in advance.
Those skilled in the art should appreciate that the security applications discussed throughout this specification are one obvious use of a target composition determination apparatus, which could be used to rapidly and non-invasively scan a target and determine its composition.
In a number of applications it would be preferable for such composition determination work to be completed in real time, such as for example, when aircraft luggage articles or products on a production line conveyor are moved past or through a scanning apparatus. In such instances it would be preferable to use a fast scanning methodology where the results obtained from the scanning system can be quickly processed to automatically provide a detection indication while the scanned target is still in the vicinity of the scanning system.
For such real time detection systems to operate, it is envisioned that the x-ray emission and detection systems would need to operate with comparatively high through put rates when compared with existing security x-ray scanning technology. In such instances a single band or energy level emission system would need to iterate through multiple energy levels for the same picture of results that would be available when the entire spectra of x-ray energies is transmitted in a single burst emission at one time.
Existing x-ray detection systems can also employ scintillator based detection systems, which convert incoming x-ray radiation to visible light energy, which is subsequently collected and amplified by a photo sensitive component. Such scintillator detectors are vulnerable to statistical uncertainty in the measurements taken, and limited in being able to resolve received x-rays with different but nearby energy levels.
It is known to provide an x-ray scanning system which measures the absorption of x-ray energy by a target across a wide spectrum of x-ray energies to determine potential composition of a target. In particular U.S. Pat. No. 6,950,492 discloses a CT focused medical composition determination system which employs an x-ray generation system to transmit a single energy level or band of x-rays at one time at a target body. Such a system is unsuitable for real time scanning applications in that the iterative, band by band approach disclosed for x-ray emissions would not allow an effective throughput of targets to be scanned in a reasonable time frame.
It would therefore be of advantage to have an improved x-ray absorption based detection system which addressed any or all of the above problems. In particular, it would be of advantage to have an x-ray absorption based detection system which could rapidly scan or investigate targets of interest, be they in security applications, or for quality control reasons in an industrial application for example. Furthermore such an x-ray absorption detection system which could resolve or distinguish between different component materials with similar x-ray absorption characteristics would also be of advantage over prior art. In particular a detection system which could automatically provide a detection indication or transmission specific to a particular material found within a target to trigger a predetermined response would also be of advantage.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.